Christian tells HELLO! of his first meeting with the Queen: "I didn't know what to expect. I was 28. I knew that this was the Queen of England, I didn't have any preconceptions.
"As soon as she walked in, the nerves dissipated, they just evaporated because she was very good at putting people at ease and she had a great sense of humour."
He recalls: "I remember talking about paintings. She said, 'What artists do you like?' and I said, 'I really like Gainsborough and Reynolds'. She said, 'I think we've got a few of those downstairs.'
"She was talking about memories of meeting people on walkabouts. She had a brilliant memory; she was very sharp, very savvy and knew what was going on and had a great interest in current events."
Before painting the Queen, Christian met with the monarch's personal dresser Angela Kelly to choose her outfit for the portrait.
"I chose the Order of the Star and Garter because that was what she was wearing on billboards. It was red, white and blue. I wanted those colours in the portrait but I wanted to go a bit closer than previous portraits that had been done, to capture that element of her character, which is the liveliness and the humour – she had a delicious sense of humour."
Christian painting the Queen at Buckingham Palace
"I chose the platform that she was going to be raised upon, the red velvet background and the flowers – I wanted flowers as it brings the outside in. The Queen chose the tiara of the Girls of Great Britain and Northern Ireland, which I think Queen Mary had given to her as a present.
"She also brought, when she came into the yellow drawing room, a shawl or a blanket. She said straight away, 'Oh, do you mind if I put this on the chair?' I said, 'No'. I knew straight away that that would reveal something about her character - that was a chance element."
Christian explains that his new diamond dust portrait of the Queen came about from a funny moment.
"The diamond dust edition is an image that's a very happy memory for me, because I said something that made her laugh. It was something probably a bit… something I shouldn't have said! But that's what a portrait sitting is – it's a bit of a time out. It's not recorded, it's intimate time."
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The artist tells us about another story from his time with the Queen, recalling: "I was talking about some of the previous depictions that had been done of her – and bear in mind I was 28 and a bit naïve. There's an Annigoni portrait where she's looking very majestic. It's lovely, but I said to her at the time, 'If you don't mind me saying, you look a little bit haughty in that picture.'
"I'm thinking about it now and thinking what the hell did I say that for?! She didn't blink, and she went, 'Well there's a reason for that.'
"She said, 'Just as you're asking me to look out the window now, Annigoni did the same thing but in this case, I was on the ground floor and there's a really high wall outside and I ended up straining to see what was over the wall. That's why I look like that in that painting.'"
Christian also remembers looking out of the window from Buckingham Palace at the crowds in the streets below. He tells us: "She said something like, 'I don't think people realise that we live here!"
"The other funny thing that happened," he continues, "Is during the sittings at the end (it was the days of film before digital cameras), I said to the Queen, 'I've got all these things, I've got to get them developed, what should I do?'
"The Queen said, 'There's a chemist over the road, that's where we go.' I thought that was funny. It was ordinariness that dissipated any nerves."
"My lasting memory of her is being very low key. She didn't like fuss. She sort of craved ordinariness but she was majestic, so she was a bit of a paradox in that sense. I hope in my portrait I captured that. It was carte blanche; I could depict her in any way. I wanted to depict her as an icon but also capture her humanity."